Change and stability in a steep morph-frequency cline in the snail Cepaea nemoralis (L.) over 43 years.

Populations of the polymorphic land snail Cepaea nemoralis (L.) from Deepdale, Derbyshire, UK, sampled in 1965-67, showed a pattern of area effects, with steep clines among groups of populations differing in shell colour and banding morph frequencies. In 2010 most of these populations were resampled. In particular a continuous transect made in 1967 of 42 18.34m x 18.34m quadrats across a steep cline in several morph frequencies was completely resampled. In the dale as a whole, yellow shells had increased in frequency. In the transect the frequencies of banding morphs showed no significant changes, but colour morphs showed some changes. Pink shells had increased in frequency in a section in which scrub had developed, and brown shells had increased in frequency in the area in which they had originally been at the highest frequency. In each case, the selection coefficients were of the order of 4%. Yellow had increased elsewhere. Nevertheless, both in the dale as a whole and in the transect...

1965至1967年间采样自英国德比郡迪普代尔（Deepdale）的多态陆地蜗牛森林蜗牛（Cepaea nemoralis (L.)）种群，呈现出区域效应（area effects）格局：不同种群间的壳色与纹型频率存在陡峭的梯度分化。
2010年，研究人员对其中绝大多数种群完成了重采样。其中尤为特殊的是，1967年针对多个纹型频率陡峭梯度设置的、由42个18.34米×18.34米样方（quadrats）组成的连续样带，得到了完整的重采样。

就整个山谷而言，黄壳个体的频率有所上升。在该样带中，纹型频率未出现显著变化，但色型频率存在一定程度的改变：粉壳个体在灌丛发育的区域频率有所升高，而棕壳个体在其原本频率最高的区域内频率同样上升。所有案例中，选择系数（selection coefficients）均约为4%。黄壳个体在其他区域的频率也有所提升。尽管如此，无论是在整个山谷还是该样带中……